Internal combustion engines typically use either a mechanical, electrical, or hydro-mechanical valve actuation system to actuate the intake and exhaust engine valves. These systems may include a combination of camshafts, rocker arms and pushrods that are driven by the engine's crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of fixed lobes on the camshaft(s).
Additional auxiliary valve events, while not required, may be desirable and are known to provide flow control of exhaust gas through an internal combustion engine in order to provide vehicle engine braking. For example, it may be desirable to actuate the exhaust valves for compression-release (CR) engine braking, bleeder engine braking, exhaust gas recirculation (EGR), brake gas recirculation (BGR), or other auxiliary valve events. However, the use of fixed cam profiles makes it difficult to adjust the timings and/or amounts of engine valve lift to optimize valve operation for various engine operating conditions.
One method of adjusting valve timing and lift given a fixed cam profile has been to incorporate a lost motion device in the valve train linkage between the valve and the cam. Lost motion is the term applied to a class of technical solutions for modifying the valve motion dictated by a fixed cam profile with a variable length mechanical, hydraulic or other linkage assembly. In a lost motion system a cam lobe may provide the maximum dwell (time) and greatest lift motion needed over a full range of engine operating conditions. A variable length system may then be included in the valve train linkage intermediate of the valve to be opened and the cam providing the maximum motion to subtract or “lose” part or all of the motion imparted by the cam to the valve. This variable length system, or lost motion system may, when expanded fully, transmit all of the cam motion to the valve and when contracted fully transmit none or a minimum amount of the cam motion to the valve.
Unfortunately, such known conventional systems may not provide the desired level of engine braking power. This is particularly true in those instances where certain engines cannot be configured with the extra parts necessary to provide the desired amount of braking power. For example, maximum engine braking power may be obtained when cams, dedicated to the valve timings and lifts needed to maximize engine braking, are provided. However, some engines do not have sufficient room or configurations to permit the inclusion of such dedicated cams. In these cases, the sole sources of engine valve movement are the fixed intake and exhaust cams. Additionally, the lobes dictated by these fixed intake and exhaust cam profiles prevent the inclusion of additional cam lobes that may otherwise be used to achieve the desired auxiliary motions.
To address these limitations, it is known in the art to leverage the different intake and exhaust valve timings between multiple cylinders to achieve the desired auxiliary valve events. In these systems, lost motion linkages are provided between the valves of one cylinder and the intake or exhaust valve motion sources of other cylinders. In a best case scenario, the auxiliary motions for a given cylinder are derived from one or more adjacent cylinders; however, it is often the case that the auxiliary motions must be derived from other, most distal cylinders. Regardless, in either case, the existence of multiple, inter-cylinder, lost motion linkages results in a relatively complex and, consequently, more expensive engine braking system.
Thus, it would be advantageous to provide solutions for engine braking and other auxiliary valve movement regimes that overcome the limitations of conventional systems.